Slotted waveguide lobing in radar system



Patented July 26, 19.69

SLOTTED WAVEGUIDE LGBING IN RADAR SYSTEM Robert E. Honer, San Diego, Calif., assignor to General Dynamics Corporation, San Diego, 'Calif., a corporation of Delaware Filed Dec. 27, 1956, Ser. No. 630,947

2 Claims. (Cl. 3'4'3--11) This invention relates to antennas, and more particularly, is concerned with a simultaneous lobing microwave antenna.

Simultaneous lobing microwave antennas heretofore known to the art have been composed of a plurality of adjacent horn radiators cooperating in pairs. Horn radiators are incapable of producing highly directional beams, and a bulky, heavy and expensive parabolic reflector is required to provide a highly directional beam.

The antenna of the present invention includes a hybrid junction associated with a waveguide linear array for transmitting a single, narrow microwave beam and, substantially simultaneously, receiving a double lobed beam having a sharp null in the same direction as the single transmitted beam.

It is, therefore, an object of the present invention to provide a simultaneous lobing antenna not requiring a parabolic reflector.

Another object of this invention is to provide a linear array which simultaneous-1y provides a single beam and a double lobe beam pattern.

Another object of this invention is to provide a waveguide linear array combined with a hybrid junction for producing a simultaneous single and double lobed beam pattern.

Another object of this invention is to provide a simultaneous lobing antenna comprising an apertured waveguide array associated with a hybrid junction for simultaneously radiating a single symmetrical directional beam and receiving a symmetrical double lobed directional beam.

Other objects and features of the present invention will appear more fully hereinafter upon consideration of the following detailed description in connection with the accompanying drawings which disclose one embodiment of the invention wherein:

Figure 1 illustrates an antenna constructed in accordance with the principles of the present invention;

Figure 2 illustrates the single lobe pattern of the; antenna; and

Figure 3 illustrates the double lobed pattern of the antenna.

An embodiment of this invention illustrated in Figure 1 includes a linear radiator 11 having a first section 12 and a mirror image second section 13 symmetrically disposed on either side of a hybrid junction 15. Hybrid junction 15 comprises a four terminal magic-T type of junction including a sum arm 16 and a difference arm 17. Sections 12 and 13 of linear radiator 11 comprise the other two arms of the magic-T junction. Linear radiator 11 and hybrid junction 15 are fabricated of hollow waveguide having dimensions suitable to the operating frequency, as is well-known to those skilled in the art.

Sections 12 and 13 of linear radiating array 11 have a plurality of radiating perforations 21 symmetrically disposed on either side of hybrid junction 15 on one wall. In the embodiment of this invention illustrated by Figure 1, perforations 21 are narrow slots cut through one of the narrow side walls of the waveguide. Exemplarily, each of sections 12 and 13 are provided with 16 slots. Slots 21 may be distributed in any manner adapted to provide a narrow beam perpendicular to the plane of the slots. Arrays suitable for employment in connection with this invention are disclosed in Microwave Antenna Theory and Design by S. Silvers, published by McGraw-Hill Book Company, Inc. in 1949. Matching terminations 34 and 35 are provided at the closed ends of sections 12 and 13 to prevent reflections and the formation of standing waves therein.

In order to transmit a narrow single beam, sum arm 16 of hybrid junction 15 is connected to a microwave transmitter 22 through a suitable transmission line 23. In the pulsed radar system illustrated, transmitter 22 may conveniently include a magnetron oscillator and suitable modulating and pulse timing circuits of a type wellknown to the art. A range receiver 24 is also connected to sum arm 16 through transmission line 23 and a suitable T-R switch 25.

Difference arm 17 of junction 15 is connected to receiver 26 through transmission line 27. Receivers 24 and 26 may conveniently be connected to a single local oscillator 33. The signals received and detected by re ceivers 24- and 26 are both applied to a discriminator 31, of a type well-known to the art. Output pulse signals from receiver 24 are also applied to a range circuit 32, along with pulses from the pulse timing circuit in transmitter 22. Suitable power supplies (not shown) provide operating potentials to the various circuits.

A train of pulses of radio-frequency energy is generated by transmitter 22 and applied to sum arm 16 by transmission line 23. Series type T-R switch 25 closes, protecting receiver 24 from the high powered energy pulse from transmitter 22. The microwave energy pulse applied to arm 16 divides equally and in phase between symmetrical branches 12 and 13 of linear radiator 11. None of the radio-frequency energy from the transmitter enters arm 17 due to the mirror symmetry between sections 12 and 13, and there is no component of field in the junction available to excite arm 17. The in-phase energy in radiating sections Hand 13 is, radiated from perforations 21. Energy is radiated by array 11 in a manner analogous to a broadside array of; dipole antennas. Accordingly, energy is radiated by array-11 in the field pattern illustrated by Figure 2. As illustrated therein, a narrow, highly directional beamis radiated, at right angles to. the array in the plane of the array.

A pulse of R.-F. energy reflected by an object in the path of the transmitted-beam is received by the twoeec; tions 12 and 13 of array 11. The received wavefront excites radiator sections 12 and 13. As is well-known to, those skilledin the art, arm. 17- of junction; 15 responds only to the difference between the signals excited in waveguide arms 12 and 13. The eifective receiving pattern is illustrated by the symmetrical double lobed figure of Figure 3. A planar wavefront arriving at array 11 perpendicular thereto excites equal energies in sections 12 and 13. The radio-frequency energy in sections 12 and 13 arrive 180 degrees out of phase at arm 17 of junction 15, thereby canceling one another and producing a null. A received planar wave traveling at an angle other than degrees excites one waveguide section in a phase relationship differing from the other waveguide section. Therefore, the signals from the two waveguide sections are not canceled out at arm 17, resulting in the angle of arrival versus amplitude response pattern illustrated in Figure 3.

Receiver 26, connected to difference arm 17 of junction 15 through transmission line 27, and to local oscil- 2,946,997 p g r lator 31, serves to detect the received diiference signal. Receiver 24 is connected to sum arm 16 of junction through transmission line 23 and T-R switch 25. Energy induced in arm 16 is the sum of the energy received by arms 12 and 13 of array 11, reciprocal to the hereinabove disclosed function during transmission of energy from the antenna. The effective amplitude versus angle of arrival relation of energy received by receiver 24 is illustrated by the single lobe pattern of Figure 2. Range circuit 32 measures the time lag between the transmission of a pulse and reception of a reflected pulse by receiver 24, and indicates the range to the reflecting object. Such a range circuit is well-known to the art, and forms no part of this invention.

'Discriminator 31 is connected to the output terminals of both of receivers 24 and 26. The'difierence inphase between the difierence signals detected by receiver 26 of the sum signals detected by receiver 24 is manifested by discriminator 31 as a direct voltage having an amplitude and polarity proportional to the difference in phase, in a manner well-known to the art. The direct voltage from discriminator 31 may be appplied to a suitable inerror angle between a line to the reflecting body and a line perpendicular to the perforated face of antenna 11 and in the plane thereof. Further, the error voltage from discriminator 31 may be applied to a suitable servo system (not shown) adapted to point the lobe of antenna 11 in the direction of the reflecting body. A directional radiation pattern in the plane perpendicular to the radiation patterns illustrated in Figures 2 and 3 may be obtained by a beam shaping horn attached to the wide surfaces of the Waveguide radiator in the manner illustrated by Figure 9.55 on page 329 of Microwave Antenna Theory and Design, disclosed hereinabove. As will be obvious to one skilled in the art, such directional patterns may also be obtained by stacking a plurality of radiators one above the other in proper phase relationship or positioning a second antenna at right angles to the antenna illustrated in Figure 1.

Although the embodiment of this invention disclosed hereinabove employs a single lobe transmitted beam pattern and both single and double lobe receiving patterns, it will be understood that the antenna may transmit or receive a single lobe or a double lobe pattern in any combination dependent upon the hybrid terminals employed in accordance with reciprocal nature of such high frequency devices.

What I claim is:

1. A directive antenna including first and second symmetrical radiating sections, each of said radiating sections comprising a rectangular waveguide having a plurality of lateral radiating slots distributed along a narrow side thereof and extending across said narrow side, the width of said slots being small with respect to the length thereof, first and second symmetrical matching terminations at the ends of said first and second symmetrical radiating sections, a magic-T waveguide junction having a first waveguide arm connected to said first radiating section, a second waveguide arm inline with said first waveguide arm connected to said second radiating section, a third waveguide arm at right angles to said first and second waveguide arms reciprocally connecting said first and second waveguide arms in phase through said waveguide junction to a transmitter and a first receiver, and a fourth waveguide arm at rightangles to said first, second and third waveguide arms reciprocally connecting said first and second waveguide arms out of phase through said Waveguide junction to a second receiver, a phase discriminator connected to said first and second receivers, and range circuits connected to said transmitter and to said first receiver.

2. A directive antenna including first and second symmetrical radiating sections, each of said radiating sections comprising a rectangular waveguide havingaplurality of lateral radiating slots distributed along a narrow side thereof and extending across said narrow side, the width of said slots being small with respect to the length thereof, first and second symmetrical matching terminationsat the ends of said first and second symmetrical radiating sections, a magic-T waveguide junction having a first waveguide arm connected to said first radiating section, a second waveguide arm in line with said first waveguide arm connected to said second radiating section, a third waveguide arm at right angles to said first and second waveguide arms reciprocally connecting said first and second waveguide arms in phase through said waveguide junction to a first radio frequency transmission line, a fourth waveguide arm at right angles to said first, second and third waveguide arms reciprocally connecting said first and second waveguide arms out of phase through said waveguide junction to a second radio frequency transmission line, a radar transmitter. connected to said first radio frequency transmission line, a series transmit-receive switch connected in said first radio fre- References Cited in the file of this patent UNITED STATES PATENTS 2,445,895 Tyrrell July 27, 1948 2,587,590 Brewer Mar. 4, 1952 2,825,057 Worthington Feb. 25, 1958 FOREIGN PATENTS 741,894 Great Britain Dec. 14, 1955 OTHER REFERENCES Silver Microwave Antenna Theory and Design (1949), McGraw-Hill, pages 286-303. 

